Why do we do systematic reviews?

This might seem a really obvious question but it’s one I really struggle with. So, this post is a request for help! Note: the post relates to systematic reviews of individual interventions as opposed to the broader outcome-focussed systematic reviews (e.g. what’s effective in helping people quit smoking?)

I get the impression that people embark on systematic reviews with little thought to the reasons behind the review; they do them because they’re expected to do one. As I look forward to the creation of robust rapid systematic reviews I can’t help feeling this needs unpicking. When you can articulate the reason for the review, you can better articulate the solution.

Also, when asking the question ‘why?’, answers such as ‘to get all the evidence’ is not a proper answer. ‘All the evidence’ is a proxy for something e.g. to allow us to accurately assess the worth of an intervention. I asked a colleague, whose opinion I respect, and she said:

“The point of an evidence synthesis is to find out what is already known about an important question”

But I feel this requires some clarification. For instance ‘Why do you want to know what is already known; to what end?’ or ‘Is it important you get all the evidence, or will a reasonably unbiased sample be sufficient?’

As I see it, people do systematic reviews for a number of possible reasons:

To know if an intervention has any ‘worth’.

To quantify, quite tightly, how good the intervention is.

To understand the adverse events associated with the intervention.

To see what has been done before, to see if new research is needed.

To improve the CV.

Bringing it back to rapid methods, for all the above reasons the issue must be ‘To what extent is it vital we get all the evidence?’. Will a reasonable sample do?

So, if you feel you understand systematic reviews please help. Also, below is a vote, where you can indicate what you feel are sensible reasons for doing a systematic review. You can tick more than one option!